El Salvador has been using the US dollar long before Venezuela and if this happens Bitcoin will also be a legal tender together with the US dollar. With that being said I don't think that their citizens will be inclined in choosing a volatile currency like Bitcoin as their main mode of payment as compared to just using USD for their daily transactions. The recognition of Bitcoin will just give them an option but they will most likely see it as an investment rather than a currency. This will also depend if how the businesses will react to this kind of change whether or not they are prepared to adopt Bitcoin as a mode of payment.
So they are having issues with their economic structure and so is the reason they are using Bitcoin as a legal tender hopefully to overcome the inflation or economic situation. There are many countries that are struggling to overcome inflation and other economic situations and those governments can come up with the plan of using Bitcoin as well as legal tender.